Budgeting for solar

by Ellen TorviSeptember 20, 2012

The cost of coal and copper -- the ingredients of conventional grid power -- are soaring. Transporting fuel to the camp or cottage is a hassle and hazardous for the off-grid enthusiast. Solar is easy and affordable for the most remote locations.

When designing an off-grid solar system we must determine the total wattage of the household in question, the nature of power usage, and its location. Companies and consumers often ask the wrong questions when thinking about alternative energy. The industry is looking to make money. The consumer is looking to get the best bang for their buck, so in the interest of the little guy who cannot fork over tens of thousands of dollars we have a few suggestions. Without getting into the nitty gritty of system sizing, wire sizing, fuse sizing everything has to be laid out in layman's terms. To design a system, you either need to know what you need to do, or how much you have to spend.

1. How much do I have to spend? Let's face it, if you only have $500 then you need to build a system that costs around $500.

2. Build a system that in the future can be expanded upon. There is no point in buying a charge controller that is just barely big enough for the system, if you expect to upgrade the system within a few years. Better to spend a bit more on a larger controller at the outset.

3. Generally, spend more on batteries and less on solar, since the solar component can be added to later more effectively than can batteries.

Addressing the foregoing: a solar system has three main components. Solar panel(s) + Charge controller + Batteries.

So for that $500 you could buy a 50 Watt panel, a 10-amp charge controller (ensure that the model is equipped with a low voltage disconnect) and a 50 amp hour battery. With this system, you can add an inverter to enable you to charge batteries for cordless tools, run a laptop or radio. You can buy pre-packed distribution centers for 12 volt lighting which have 12 volt auto-jacks and 2.1 plug-ins to run lighting. A system this size would give you 25 amp hours of continuous power. Roughly, a 50 Watt panel will charge a 50 Amp/h battery in a day of continuous sunlight. Using ruggedized cases, we have portable systems that can be easily transported -- just thrown into the back of a pick-up truck or the trunk of a car.

Consider the loads that you will be using, and start your system design with load selection. For example, the solar system required to run a desktop computer will be a lot bigger than one to run a laptop or tablet computer, and it may be smarter to buy a new computer to save money on the system. Similarly with lighting--LED bulbs are ideal for lighting from your 12V solar system where minimal energy consumption is a concern because LED bulbs can provide meaningful light with as little as 1 Watt of power consumption (100 lumens per watt).

To expand on your $500 system you can substitute your 50W panel up to a 135 Watt panel keeping your 10-amp charge controller. You can upgrade your batteries from a 50 Amp/h battery to a 106 Amp/h or even a 165 amp/h battery. A larger system could power a 12-volt refrigerator/freezer and ensure a supply of cold beer at the off-grid cottage. Of course, systems can become as large as necessary to meet any given set of loads and usage.